Download and install VMware vCenter Converter for Windows and install it on the physical Windows XP or higher machine to be converted.
Run the VMware Converter on the physical host. It will take sometime to run and possibly may create multiple vmdk files.
Transfer the converted virtual machine files to the destination host from the external drive. The Windows 7 physical machine is no longer needed. The rest of this process is performed on the destination host – Linux in this case. The .vmx file is not needed.
In VirtualBox, create a new guest and select an existing hard disk to attach. Be certain to select the .vmdk and not one of the slices.
Once the guest is created, edit the settings. Select the System motherboard settings and adjust the amount of base memory. I suggest a minimum of 2GB of RAM if the host has enough to run stable. Enable PAE/NX on the processor tab. Enable VT-x/AMD-V and Nested Paging, on the display settings I gave it 128 MB of video memory and enabled 3D and 2D acceleration.
On the storage settings, I removed the default SATA controller and added a SCSI controller. Re-attach the guest .vmdk at this time to the new controller. Check Use host I/O cache.
Select the default NAT network adapter.
The guest virtual machine should now start up without problems. If you do have problems, tweak the settings for the VM until you achieve success.
The first time I booted the Windows 7 virtual machine, it will prompt you to install the Virtualbox guest additions. You will want to do this to achieve optimal performance. Reboot the virtual machine and you should be good to go!